Comparison of Standard Methods for Critical Pitting Temperature Testing of Anticorrosion Alloys

Three standard methods for critical pitting temperature (CPT) testing, weight loss method, potentiostatic method and potentiodynamic method, were compared to study their characteristics and adaptability. The effects of different test environments and methods on CPT determination of S22053 duplex stainless steel were emphatically studied. The results show that CPT values tested by three methods for S22053 duplex stainless steel were different, which were 35.6, 53.1, and 55℃, respectively, because of different experimental conditions and critical conditions for determining pitting corrosion. Due to the harsh test environment used in the weight loss method, the CPT measured by the weight loss method was much lower than that measured by the potentiostatic method and the potentiodynamic method. The weight loss method needs a long test time and can not accurately describe the pitting formation process for a single material, but has low equipment requirements and is easy to operate. The potentiodynamic method and potentiostatic method have high requirements for equipment, especially the potentiostatic method. The heating rate and the temperature gradient in the solution have an effect on the test results, but the measurement parameters both in the potentiodynamic method and in the potentiostatic method can accurately reflect the critical conditions for the formation of steady-state pitting corrosion. The potentiostatic method also has the advantages of less sample number, short test time and measured CPT as a specific value.